IJOER-JUL-2017-9

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A Study on Seismic Response of an Irregular Structure with Different Angle of Incidence

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International Journal of Engineering Research Science IJOER ISSN: 2395-6992 Vol-3 Issue-7 July- 2017 Page | 90 A Study on Seismic Response of an Irregular Structure with Different Angle of Incidence Thanuja D 1 Manohar K 2 1 Department of Civil Engineering Sahyadri College of Engineering and Management VTU University Belagavi - 590 018 2 Assistant Professor Department of Civil Engineering Sahyadri College of Engineering and Management VTU University Belagavi - 590 018 Abstract — Earthquakes are a natural calamity feared by most and cause great destruction in and around the seismic zone where they occur. In seismic design of buildings the earthquake motions are considered in principle directions of building which may not be true in all cases. The present study is focused on the earthquake incidence angle and its effect on the structure’s column axial force and to obtain the critical angle using Non Linear Time History Analysis. A set of values from 0 to 90 degrees with an increment of 10 degrees have been used for angle of excitation. An asymmetrical structure of 10 storeys was considered. It can see that the critical angle may vary the column axial force from column to column. The models are analysed using ETABS 15 software. The structural parameters such as column axial force displacement and story shear in columns are studied. The paper concludes that the internal forces of structural elements depend on the angle of incidence of seismic wave data. There are different critical angles for different parameters not necessarily that it should be the same of the column axial force. Keywords — Incidence angle Non Linear Time History Column axial force Displacement Story shear. I. INTRODUCTION Earthquakes are natural hazards under which disasters are mainly caused by damage to or collapse of buildings and other man-made structures. Experience has shown that for new constructions establishing earthquake resistant regulations and their implementation is the critical safeguard against earthquake-induced damage. As regards existing structures it is necessary to evaluate and strengthen them based on evaluation criteria before an earthquake. Earthquake damage depends on many parameters including intensity duration and frequency content of ground motion geologic and soil condition quality of construction etc. Building design must be such as to ensure that the building has adequate strength high ductility and will remain as one unit even while subjected to very large deformation. Sociologic factors are also important such as density of population time of day of the earthquake occurrence and community preparedness for the possibility of such an event. Up to now we can do little to diminish direct earthquake effects. However we can do much to reduce risks and thereby reduce disasters provided we design and build or strengthen the buildings so as to minimize the losses based on the knowledge of the earthquake performance of different building types during an earthquake. Observation of structural performance of buildings during an earthquake can clearly identify the strong and weak aspects of the design as well as the desirable qualities of materials and techniques of construction and site selection. The study of damage therefore provides an important step in the evolution of strengthening measures for different types of buildings. 1.1 Earthquake Incidence Angle Earthquakes are well known for the damage and destruction that they leave behind. Present scenario demands the need for designing the structures to withstand seismic forces. In seismic design of structures the earthquake motions are considered in principle directions of structure. Insalmostdall seismic design codes consideration of simultaneous effects of two horizontal components of earthquake excitations is taken into account by applying 100 of earthquake lateral forces in the direction of one of the structure main axes and 30 of those forces in the direction of other main axis. In reality the direction of the dominant component of excitations might not be one of the main directions of the structure axes and applying the main component in a direction other than main axes direction may lead to higher internal forces and stresses in the structure’s

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International Journal of Engineering Research Science IJOER ISSN: 2395-6992 Vol-3 Issue-7 July- 2017 Page | 91 structural elements. Therefore the structure should be resistant under different excitation angles of earthquake. Some researchers have worked on the effect of angle of excitation on the response values since mid-80s. Over the period of time Time History Analysis has become an important tool is assessing the behavior of a structure subjected to seismic loads. Time History Analysis is a method by which earth motion input of a particular earthquake can be used to determine the response of the structure. The main advantage of using this method is that the accuracy of the system response is higher when compared to Response Spectrum analysis as the actual earth motion record from an earthquake can be used to simulate the structure. II. METHODOLOGY 2.1 Project Details Multi-storeyed apartment Safe bearing capacity of soil SBC 300 KN/mm2 Height of each floor 2.95m typicalHeight of basement 3.3mHeight of ground floor 4.05mTotal height of the structure 41.4m Software E-Tabs AutoCAD. The structure given is to be used for residential purpose. Basement + Earth+ 13 Upper Floors + Overhead Water tank. The height of the basement and earth floor is 3.3m and typical floor height is 2.95 m .Total height of the structure is 41.1m above the plinth and each floor of the structure comprises of six houses where four of them have one Living room one Master Bedroom and two other Bedrooms with three toilets one foyer one Kitchen and one Dining room one balcony and one utility and two of them have one Living room one Master Bedroom and one Bedroom with two toilets one foyer one Kitchen and one Dining room one balcony and one utility. FIG. 1: E-TABS MODEL- PLAN FIG. 2: E-TABS MODEL- 3D III. RESULTS AND DISCUSSION The results of Time History Analysis in the form of maximum column forces column moments maximum displacement and storey shear were studied. 3.1 Maximum Column Forces The values of maximum column forces and the variation with incidence angle is shown in Table 1.The max column force was found to be -3693.42 kN for the load combination 1.5TDL-ELX-0.3ELY Max for column C-20 at the basement-1at 70 0 angle.

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International Journal of Engineering Research Science IJOER ISSN: 2395-6992 Vol-3 Issue-7 July- 2017 Page | 92 TABLE 4.1 COLUMN FORCES FOR ALL THE ANGLE OF INCIDENCE 0°- 90° Story Column Unique Name Load Case/Combo P Angle kN Deg. Basement-1 C20 2578 0.9TDL+1.50.3THX-THY Min -2217.3 0 Basement-1 C20 2578 1.2TLD+LL+0.3THX-TY Min -3232.67 0 Basement-1 C20 2578 1.5TDL+0.3EX-EY Min -3693.38 0 Basement-1 C20 2578 0.9TDL+1.50.3THX-THY Min -2217.35 10 Basement-1 C20 2578 1.2TLD+LL+0.3THX-TY Min -3232.7 10 Basement-1 C20 2578 1.5TDL+0.3EX-EY Min -3693.42 10 Basement-1 C20 2578 0.9TDL+1.5-0.3THX-THY Min -2217.33 20 Basement-1 C20 2578 1.2TLD+LL-0.3THX-TY Min -3232.69 20 Basement-1 C20 2578 1.5TDL-0.3EX-EY Min -3693.41 20 Basement-1 C20 2578 0.9TDL+1.5-0.3THX-THY Min -2217.24 30 Basement-1 C20 2578 1.2TLD+LL-0.3THX-TY Min -3232.62 30 Basement-1 C20 2578 1.5TDL-0.3EX-EY Min -3693.32 30 Basement-1 C20 2578 0.9TDL+1.5-0.3THX-THY Min -2217.05 40 Basement-1 C20 2578 1.2TLD+LL-0.3THX-TY Min -3232.47 40 Basement-1 C20 2578 1.5TDL-0.3EX-EY Min -3693.13 40 Basement-1 C20 2578 0.9TDL+1.5-THX-0.3THY Min -2217.11 50 Basement-1 C20 2578 1.2TLD+LL-THX-0.3TY Min -3232.51 50 Basement-1 C20 2578 1.5TDL-0.3EX-EY Min -3692.85 50 Basement-1 C20 2578 0.9TDL+1.5-THX-0.3THY Min -2217.27 60 Basement-1 C20 2578 1.2TLD+LL-THX-0.3TY Min -3232.64 60 Basement-1 C20 2578 1.5TDL-EX-0.3EY Min -3693.35 60 Basement-1 C20 2578 0.9TDL+1.5-THX-0.3THY Min -2217.34 70 Basement-1 C20 2578 1.2TLD+LL-THX-0.3TY Min -3232.7 70 Basement-1 C20 2578 1.5TDL-EX-0.3EY Min -3693.42 70 Basement-1 C20 2578 0.9TDL+1.5-THX+0.3THY Min -2217.37 80 Basement-1 C20 2578 1.2TLD+LL-THX+0.3TY Min -3232.72 80 Basement-1 C20 2578 1.5TDL-0.3EX+EY Min -3691.77 80 Basement-1 C20 2578 0.9TDL+1.5-THX-0.3THY Min -2217.3 90 Basement-1 C20 2578 1.2TLD+LL-THX-0.3TY Min -3232.67 90 Basement-1 C20 2578 1.5TDL-EX-0.3EY Min -3693.38 90

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International Journal of Engineering Research Science IJOER ISSN: 2395-6992 Vol-3 Issue-7 July- 2017 Page | 93 3.2 Maximum Column Moments The values of maximum column moments and the variation with incidence angle is shown in Table 2. The maximum moment was in 1ST FLOOR for the column C-32 with the load combination 1.2TLD+LL-0.3THX+TY Max of 225.3083 kN-m for an incidence angle of 80°. TABLE 2 COLUMN MOMENTS FOR ALL THE ANGLE OF INCIDENCE 0°- 90° Story Column Load Case/Combo P M3 Angle kN kN-m Deg. Ground floor C32 0.9TDL+1.5THX-0.3THY Min -1621.179 -95.8313 0 1st Floor C32 1.2TLD+LL-THX+0.3TY Max -2028.8649 225.2589 0 Ground floor C32 1.5TDL+EX+0.3EY Min -2696.5294 -159.1 0 Ground floor C32 0.9TDL+1.5THX-0.3THY Min -1621.3585 -95.8373 10 1st Floor C32 1.2TLD+LL-THX+0.3TY Max -2028.8187 225.2588 10 Ground floor C32 1.5TDL+EX+0.3EY Min -2696.6017 -159.108 10 Ground floor C32 0.9TDL+1.5THX+0.3THY Min -1621.3182 -95.8335 20 1st Floor C32 1.2TLD+LL-THX+0.3TY Max -2028.913 225.2804 20 1st Floor C32 1.5TDL-EX+0.3EY Max -2211.2698 150.3738 20 Ground floor C32 0.9TDL+1.5THX+0.3THY Min -1621.2853 -95.8191 30 1st Floor C32 1.2TLD+LL-THX+0.3TY Max -2028.8427 225.2352 30 Ground floor C167 1.5TDL-EX+0.3EY Min -469.6913 -239.32 30 Ground floor C32 0.9TDL+1.5THX+0.3THY Min -1621.0826 -95.7812 40 1st Floor C32 1.2TLD+LL-THX+0.3TY Max -2028.9545 225.1234 40 Basement-1 C32 1.5TDL-0.3EX-EY Min -2966.8733 -70.2712 40 Ground floor C32 0.9TDL+1.5THX+0.3THY Min -1620.7625 -95.7169 50 1st Floor C32 1.2TLD+LL-0.3THX+TY Max -2029.8786 225.0561 50 Basement-1 C32 1.5TDL-0.3EX-EY Min -2967.814 -70.4311 50 Ground floor C32 0.9TDL+1.5-0.3THX-THY Min -1619.9548 -95.7232 60 1st Floor C32 1.2TLD+LL-0.3THX+TY Max -2029.4102 225.2217 60 Basement-1 C32 1.5TDL-0.3EX-EY Min -2968.5768 -70.5425 60 1st Floor C32 0.9TDL+1.5-0.3THX+THY Max -1324.0325 91.6141 70 1st Floor C32 1.2TLD+LL-0.3THX+TY Max -2029.1073 225.3066 70 Ground floor C32 1.5TDL+0.3EX-EY Min -2696.2622 -159.065 70 1st Floor C32 0.9TDL+1.5-0.3THX+THY Max -1323.8518 91.6161 80 1st Floor C32 1.2TLD+LL-0.3THX+TY Max -2028.9627 225.3083 80 Ground floor C32 1.5TDL+0.3EX-EY Min -2696.497 -159.082 80 Ground floor C32 0.9TDL+1.50.3THX-THY Min -1621.1683 -95.8352 90 1st Floor C32 1.2TLD+LL+0.3THX+TY Max -2028.8649 225.2589 90 Ground floor C32 1.5TDL+0.3EX-EY Min -2696.5294 -159.1 90

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International Journal of Engineering Research Science IJOER ISSN: 2395-6992 Vol-3 Issue-7 July- 2017 Page | 94 3.3 Maximum Story Displacement The values of maximum story displacement and the Comparison between displacements for different angles is shown in Figure 3 and Table 3.Displacement is more in 40° in x-direction 5.47mm and 20°in y-direction 2.73mm for the combo 1.5TDL+0.3EX-EY. TABLE 3 COMPARISON BETWEEN DISPLACEMENTS FOR DIFFERENT ANGLES Angle X directionmm Y directionmm 10 2.58 5.63 20 2.73 5.76 30 2.84 5.47 40 2.96 5.47 50 2.81 5.39 60 2.7 5.49 70 2.5 5.53 80 2.56 5.54 90 2.503 5.526 FIGURE 3: COMPARISON BETWEEN DISPLACEMENTS FOR DIFFERENT ANGLES 3.4 Maximum Story Shear The values of maximum story shear and the Comparison between story shear for different angles is shown in Figure 4 and Table 4. Story shear is more in 70° with 128 kN in x-direction and 50° with 105kN in y-direction for the combo 1.5TDL+0.3EX-EY. TABLE 4 COMPARISON BETWEEN STORY SHEAR FOR DIFFERENT ANGLES Angle X directionkN Y direction kN 10 128 57 20 127 73 30 123.6 87 40 115 101 50 120 105 60 126 93 70 128 78 80 126 61 90 126 46 2.58 2.73 2.84 2.96 2.81 2.7 2.5 2.56 2.503 5.63 5.76 5.47 5.47 5.39 5.49 5.53 5.54 5.526 0 1 2 3 4 5 6 7 10 20 30 40 50 60 70 80 90 Displacement in mm Angle of incidence DISPLACEMENT X direction Y direction

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International Journal of Engineering Research Science IJOER ISSN: 2395-6992 Vol-3 Issue-7 July- 2017 Page | 95 FIGURE 4: COMPARISON BETWEEN STORY SHEAR FOR DIFFERENT ANGLES IV. CONCLUSION  The internal forces of structural elements depend on the angle of incidence of seismic wave data.  There are different critical angles for different parameters not necessarily that it should be the same of the column axial force.  The maximum displacement and maximum column axial forces are of same angle i.e. 70° for EL CENTRO earthquake data.  The critical angle depends on the geometry of the structure.  The objective of this study is to highlight that the earthquake motions are considered in principle directions of structure but excitations might not be in one of the main directions of the structure axes. REFERENCES 1 Bhatnagar U. “Seismic performance on skewed bridges under orthogonal earth motion components” Journal of Structural Engineering 2013 pp.1-94. 2 Salemi M. H. “Studying the Effect of Earthquake Excitation Angle on the Internal Forces of Steel Structures Elements by Using Non Linear Time History Analysis”. 14th World Conference on Earthquake Engineering 2008 pp.1-8. 3 Poursha F. K.”Responses of Three Dimensional Structures under Bidirectional and Unidirectional Seismic Excitations”. 13th World Conference on Earthquake Engineering 2004 No 55. 4 M. Sri Kanya “Effect of Earthquake Incidence Angle on Seismic Performance of RC Buildings”. International Journal of Research in Engineering and Technology vol 4 Issue 13 2006 pp.156-161. 5 M. Sri Kanya 2006 “Effect of Earthquake Incidence Angle on Seismic Performance of RC Buildings”. International Journal of Research in Engineering and Technology vol 4 Issue 13 pp.156-161. 128 127 123.6 115 120 126 128 126 126 57 73 87 101 105 93 78 61 46 0 20 40 60 80 100 120 140 10 20 30 40 50 60 70 80 90 Story Shear kN Angle of incidence STORY SHEAR X directionkN Y direction kN

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